a) Field of the Invention
The present invention relates to a semiconductor device having a resin molded LSI chip mounted on a circuit board with wiring patterns.
b) Description of the Related Art
As one of LSI packages, there is a chip carrier package suitable for a device having multiple connection pins. For example, an LSI chip is mounted on the front surface of a circuit board. The circuit board has wiring patterns on the front surface thereof and associated wiring patterns and solder balls on the rear surface thereof, and is resin-molded for hermetically sealing the LSI chip. This type of package, called a Ball Grid Array (BOA) package, has been proposed in U.S. Pat. No. 5,241,133, which is incorporated herein by reference.
With this BGA package, an LSI ship is mounted on one surface of a circuit board and hermetically sealed by resin. This type of package has the following problems.
First, a circuit board warps because of compression of molding. This warp may be considered resulting mainly from a difference between thermal expansion coefficients between the circuit board and sealing resin layer. As the size of a circuit board becomes large, the co-planarity of a number of solder balls becomes poor and packaging defects are likely to occur.
Second, moisture content is likely to permeate into the device from lower peripheries of a region of a circuit board (particularly plastic circuit board) for mounting an LSI chip or from through holes formed in the board. Device defects caused by moisture is therefore likely to occur.
Third, if moisture content permeates into the package, a process of drying a package at a high temperature is required during packaging processes. This high temperature process easily causes peeling-off of the sealing resin layer and the circuit board.